As for heterocyclic compounds, compounds in which two heterocycles are condensed to a benzene ring are hitherto known (see, for example, JP-A-63-150273 (“JP-A” means unexamined published Japanese patent application), JP-A-4-85547, JP-T-5-506428 (“JP-T” means published Japanese translation of PCT application), and Journal of the American Chemical Society, 1995, Vol. 117, pages 9995 to 10002). In these publications, there are disclosures relating to tetrathiafulvalene analogs probably because these heterocyclic compounds interested mainly in a charge-transfer complex. Therefore, a majority of the condensed heterocycles disclosed therein is dithiol rings. More specifically, most of the dithiol rings are those having a structure wherein an alkylmercapto group or a dithiol ring is substituted via exomethylene at 2-position of the dithiol ring.
Further, with respect to the use of these compounds having such a structure for various kinds of functional materials, there are one case where these compounds are used as a charge-transfer complex for use in an organic electrophotographic material (see, for example, JP-A-4-85547), and another case where these compounds are used as an inert carbon free radical partial structure (see, for example, JP-T-5-506428). However, these structures are limited to a narrow scope whereby desirable properties can be provided. Since then, new compounds have not been found, probably because studies on other applications of the dithiol rings have not been tried.
Ultraviolet absorbents have been used in combination with various resins for providing the resins with ultraviolet-absorptivity. Both inorganic and organic ultraviolet absorbents are used as the ultraviolet absorbent. The inorganic ultraviolet absorbents (see, for example, JP-A-5-339033, JP-A-5-345639 and JP-A-6-56466) are superior in durability properties such as weather resistance and heat resistance. However, the freedom in selecting the compound is limited, because the absorption wavelength is determined by the band gap of the compound. In addition, there is no inorganic absorbent that absorbs the light in a long-wavelength ultraviolet (UV-A) range of around 400 nm. And any such absorbent that absorbs long-wavelength ultraviolet would have color because it would have absorption also in the visible range.
In contrast, the freedom in designing the absorbent structure is much wider for organic ultraviolet absorbents, and thus, it is possible to obtain absorbents having various absorption wavelengths by designing the absorbent chemical structure properly.
Various organic ultraviolet absorbent systems have been studied, and for absorption in the long-wavelength ultraviolet range, it is conceivable either to use an absorbent having the wavelength of maximal absorption in the long-wavelength ultraviolet range or to use a high concentration of absorbent. However, the absorbents described in, for example, JP-A-6-145387 and JP-A-2003-177235 having the wavelength of maximal absorption in the long-wavelength ultraviolet range are inferior in light stability, and their absorption capacity declines over time.
In contrast, benzophenone- and benzotriazole-based ultraviolet absorbents are relatively higher in light stability, and increase in concentration or film thickness leads to relatively clean blocking of the light in the longer-wavelength range (see, for example, JP-T-2005-517787 and JP-A-7-285927). However, when such an ultraviolet absorbent is applied as mixed with a resin or the like, the film thickness is limited to several tens of μm at the most. For utilizing the film thickness to block the light in the longer-wavelength range, it is necessary to add the ultraviolet absorbent to a considerably high concentration. However, simple increase in concentration only results in a problem of precipitation and bleed-out of the ultraviolet absorbent during long-term use. In addition, among benzophenone-based and benzotriazole-based ultraviolet absorbents, there are some ultraviolet absorbents that may cause concern about skin irritation and accumulation in body. Therefore, intensive care should have been given to these compounds during use.
Meanwhile, as for the heterocyclic compound, compounds represented by any one of the following Formulae (S-1) to (S-5) are known (see, for example, JP-A-63-150273, Tetrahedron Letters, 1977, Vol. 26, page 2223). These compounds interested only in a charge-transfer complex component and an intermediate thereof. In fact, these compounds absorb little visible light in solution. Therefore, they have never been considered the use for a coloring agent.
